Electrical submersible pump

ABSTRACT

A method and apparatus for lifting fluids from a well is provided. In one embodiment, a pump assembly comprises a rotary motor adapted to actuate a reciprocating pump. The motor shaft of the rotary motor is threadedly coupled to a drive member of the reciprocating pump. In operation, rotation of the rotary motor causes reciprocation of the reciprocating pump.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to a pumping apparatus for transporting fluids from a well formation to the earth's surface. Particularly, embodiments of the present invention relate to an electrical submersible pump assembly having a positive displacement pump driven by a rotary motor. More particularly, embodiments of the present invention relate to a pump assembly having a rotary motor capable of rotating in two directions.

2. Description of the Related Art

Many hydrocarbon wells are unable to produce at commercially viable levels without assistance in lifting formation fluids to the earth's surface. In some instances, high fluid viscosity inhibits fluid flow to the surface. More commonly, formation pressure is inadequate to drive fluids upward in the wellbore. In the case of deeper wells, extraordinary hydrostatic head acts downwardly against the formation, thereby inhibiting the unassisted flow of production fluid to the surface.

In wells that produce natural gas, liquids are often carried with the gas into the well bore. These liquids accumulate in the well bore and fill the well casing. The rise of the liquid level in the casing leads to a pressure increase of the liquid in the casing, which may shut off the flow of gas unless the liquid is removed.

A common approach for urging production fluids to the surface includes the use of a mechanically actuated, positive displacement pump. Mechanically actuated pumps are sometimes referred to as “sucker rod” pumps. The reason is that reciprocal movement of the pump necessary for positive displacement is induced through reciprocal movement of a string of sucker rods above the pump from the surface.

A sucker rod pumping installation consists of a positive displacement pump disposed within the lower portion of the production tubing. The installation includes a piston which is moved in linear translation within the tubing by means of steel or fiberglass sucker rods. Linear movement of the sucker rods is typically imparted from the surface by a rocker-type structure. The rocker-type structure serves to-alternately raise and lower the sucker rods, thereby imparting reciprocating movement to the piston within the pump downhole.

Other methods are currently used to remove the water from the casing. These methods include use of chemical foams, progressive cavity pumps (“PCP”), conventional Electric Submersible Pumps (“ESP”), and other forms of artificial lift. Conventional ESPs pump the fluid by imparting centrifugal force on the fluid. The lift H provided by a centrifugal pump is a square function of the ratio of the diameter D, i.e., H₂=H₁(D₂/D₁)². Thus, a smaller diameter pump will require more stages to lift the fluid at the same rate from the same depth.

Many existing gas fields are completed with small diameter tubing in the gas producing zone where the water accumulates. The completion requires a small diameter to be installed in this section of the casing to remove the liquid. In these applications, the pump diameter is often restricted to a 2 inch diameter. In comparison, the smallest traditional ESP has a 3.35 inch diameter. Thus, a 2 inch diameter ESP would require many more stages to lift the fluid in the oil well.

To overcome the limitations of a centrifugal pump driven by an electric motor, efforts have been made to develop a linear electric motor for use downhole to drive a positive displacement pump. Positive displacement pump are more efficient in lifting fluids from high depths in small diameter pipes than centrifugal pumps. One example of a linear motor is disclosed in U.S. Pat. No. 5,252,043, issued to Bolding, et al., entitled “Linear Motor-Pump Assembly and Method of Using Same.” Other examples include U.S. Pat. No. 4,687,054, issued in 1987 to Russell, et al. entitled “Linear Electric Motor For Downhole Use,” and U.S. Pat. No. 5,620,048, issued in 1997, and entitled “Oil-Well Installation Fitted With A Bottom-Well Electric Pump.” In these examples, the pump includes a linear electric motor having a series of windings which act upon an armature. The pump is powered by an electric cable extending from the surface to the bottom of the well, and residing in the annular space between the tubing and the casing. The power supply generates a magnetic field within the coils which, in turn, imparts an oscillating field upon the armature. In the case of a linear electric motor, the armature is translated in an up-and-down fashion within the well. The armature, in turn, imparts translational movement to the pump piston residing below the motor. The piston enables a positive displacement pump to displace fluids up the wellbore and to the surface with each stroke of the piston.

Submersible pump assemblies which utilize a linear electric motor face many challenges during their employment. A first problem relates to the introduction of the submersible pump into the wellbore. As noted, wellbores tend to have inherent deviations. At the same time, submersible pumps can be of such a length that it becomes difficult for the pump to negotiate turns and bends within the tubing string of the well. The length of a linear submersible pump is generally proportional to the horsepower desired to be generated by the pump assembly. Greater horsepower would be needed for deeper wells in order to overcome the prevailing hydrostatic head. This, in turn, would require a greater length or number of windings within the stator and corresponding armature.

Another problem inherent in current submersible pump designs pertains to the restricted diameter for fluid flow within the motor section. In linear submersible pump designs, the motor portion of the pump is configured above the piston and sucker rod pump portion. The result is that fluid being displaced by the pump must travel through restrictive fluid ports which reside within the armature portion of the motor en route to the surface. Typically, the inner diameter of the production string defines an already narrow path of flow through which production fluids must travel. Positioning a linear electric motor within the tubing creates a further restriction for fluid movement.

There is a need, therefore, for an improved submersible electrical pump. There is also a need for an electrical submersible pump operated by a rotary motor.

SUMMARY OF THE INVENTION

In one embodiment, a pump assembly comprises a rotary motor adapted to actuate a reciprocating pump. The rotary motor is coupled to the reciprocating pump using a ball screw type connection. In operation, rotation of the rotary motor causes a reciprocating action of the reciprocating pump.

In another embodiment, the rotary motor comprises a permanent magnet motor. The rotary motor is adapted to rotate in two different directions, thereby causing the reciprocating action of the reciprocating pump. In another embodiment still, the reciprocating pump comprises a positive displacement pump.

In another embodiment, a method of lifting fluids from a wellbore comprises providing a pump assembly having a reciprocating pump actuated by a rotary motor; positioning the pump assembly in the wellbore; operating the rotary motor to actuate the reciprocating pump; and lifting fluids from the wellbore.

In another embodiment still, the reciprocating pump includes a drive member threadedly coupled to a motor shaft of the rotary motor. In operation, rotation of the motor shaft causes the drive member to move along the motor shaft. In yet another embodiment, the rotary motor is cycled between two rotational directions to drive the reciprocating action of the pump.

In another embodiment still, a pump assembly comprising a rotary motor is disposed below a subsurface safety valve. Preferably, the rotary motor is capable of rotating in two directions. More preferably, the rotary motor comprises a permanent magnet motor.

In another embodiment still, a pump assembly comprises a pump adapted to pump a fluid between at least two fluid cavities and a rotary motor adapted to actuate the pump, wherein a direction of fluid flow between the at least two fluid cavities is reversed by changing a rotational direction of the rotary motor. In yet another embodiment, each of the fluid cavities is expandable. In yet another embodiment, expansion or retraction of the fluid cavity controls movement of a pumped fluid in the chamber.

In another embodiment still, a method of lifting fluids from a wellbore, comprises providing a pump assembly having a rotary motor and a fluid chamber; rotating the rotary motor in a first direction to introduce fluid into the fluid chamber; rotating the rotary motor in a second direction to discharge fluid from the fluid chamber; and lifting the discharge fluid from the wellbore. In yet another embodiment, the pump assembly comprises a second fluid chamber, wherein the second fluid chamber is discharging fluid while fluid chamber is accumulating fluid. In yet another embodiment, the method further comprises discharging fluid from a second chamber while the fluid is being introduced into the fluid chamber. In yet another embodiment, the method further comprises expanding an expandable member in the fluid chamber while fluid is being discharged from the fluid chamber. In yet another embodiment, the method further comprises retracting an expandable member in the fluid chamber while fluid is being introduced into the fluid chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a schematic of an embodiment of an electrical submersible pump disposed in a wellbore below a subsurface safety valve.

FIG. 2 is a partial cross-section view of the pump of FIG. 1.

FIG. 2A is a partial cross-section view of another embodiment of a pump.

FIG. 3 is another embodiment of a check valve assembly used with an electrical submersible pump assembly.

FIG. 4 is yet another embodiment of an electrical submersible pump assembly. This embodiment features a double acting pumping mechanism. One pump positioned below the electric motor and one pump positioned above electric motor.

FIG. 5 is another embodiment of a pump assembly.

FIG. 6 is yet another embodiment of a pump assembly.

DETAILED DESCRIPTION

A method and apparatus for lifting fluids from a well is provided. In one embodiment, a pump assembly comprises a rotary motor adapted to actuate a reciprocating pump. The motor shaft of the rotary motor is coupled to a drive member of the reciprocating pump. In operation, rotation of the rotary motor causes reciprocation of the reciprocating pump.

FIG. 1 is a partial cross-section view of a wellbore 10. A casing 15 is fixed in the wellbore 10 by cured cement. The casing 10 is perforated to allow the inflow of formation fluids. A string of production tubing 20 extends from the surface to a subsurface safety valve 170. The production tubing 20 then extends below the subsurface safety valve 170 to the production zone. The production tubing 20 includes an electrical submersible pump 100 disposed at its lower end. The pump 100 is being reciprocated by a submersible, rotary electrical motor 110. Preferably, the motor 110 is disposed below the pump 100 so that formation fluids may be discharged directly into the production tubing 20. A power cable 175 extends from the surface to provide power to the motor 110.

FIG. 2 is a partial cross-section view of the wellbore 10. In this view, an embodiment of the electrical submersible pump 100 is shown in greater detail. The pump 100 is operated by a rotary motor 110. Preferably, the rotary motor 110 is a permanent magnet electric motor. An exemplary permanent magnet electric motor suitable for use with the pump 100 is disclosed in U.S. Pat. No. 5,923,111 issued to Eno, et al., which patent is herein incorporated by reference in its entirety. Other suitable rotary motors known to a person of ordinary skill are also contemplated.

A motor seal 115 may be used to couple the motor 110 to the pump 100. The motor seal 115 allows for oil expansion as the pump 100 is reciprocated. Preferably, the motor seal 115 is a barrier type seal having a metal bellow or an elastomeric diaphragm or bag. Other suitable motor seals known to a person of ordinary skill are also contemplated.

In one embodiment, the pump 100 includes a housing 112 having one or more ports 113 for fluid communication with the wellbore 10. An expandable member 120 in the housing 112 fluidly seals off an interior portion 111 of the pump 100 from the wellbore fluids. Suitable expandable members include a diaphragm and a bellow.

The expandable member 120 is retracted or expanded using a ball screw type coupling with the motor shaft 125 of the motor 110. As shown in FIG. 2, a drive member 130, such as a nut, is threadedly connected to the motor shaft 125. One or more extension members 132 connect the nut 130 to a plate 122 of the expandable member 120. In this respect, rotation of the motor shaft 125 drives the nut 130 to move axially along the motor shaft 125. In turn, the extension members 132 transfer the movement to the plate 122, thereby causing extension or retraction of the expandable member 120, also referred to as reciprocation. The nut 130 may include a guide member such as a centralizer 135 to facilitate its movement along the motor shaft 125. In one embodiment, the centralizer 135 may be guided in the wall of the housing 112. In this respect, the centralizer 135 will ensure axial movement of the nut 130 relative to the motor shaft 125 as the motor shaft 125 is rotated. The interior portion 111 of the pump 100 may be filled with oil to provide a clean oil operating environment for the drive member 130. The oil volume in the interior portion 111 changes as the plate 122 moves linearly. The change in the oil volume is compensated by the motor seal 115. In another embodiment, the change in oil volume may be compensated by a second expandable member coupled to the motor 110, thereby allowing the pump 100 to operate without the need of the motor seal 115.

A reciprocating member 140 connected to the plate 122 extends from the plate 122 and into an upper portion of the housing 112. The reciprocating member 140 includes an arm portion 143 and a valve portion 142. The valve portion 142, also known as the traveling valve, is adapted to selectively control the flow of wellbore fluids into and out of the fluid chamber 145. The fluid chamber 145 is defined by the traveling valve 142, a standing valve 150 and the housing 112. Each of the traveling valve 142 and the standing valve 150 includes a seat for mating with a seal member 141, 151. An exemplary seal member is a ball. The traveling valve 142 is adapted to allow inflow to the fluid chamber 145, while the standing valve 150 is adapted to allow outflow from the fluid chamber 145. The arm portion 143 is adapted and arranged to maintain the traveling valve 142 above the ports 113 such that during the downstroke, wellbore fluids entering the ports 113 may flow through the traveling valve 142 and into the fluid chamber 145.

In operation, the pump 100 acts as a reciprocating positive displacement pump to deliver wellbore fluids to the surface. As shown in FIG. 2, the pump 100 is in the beginning of its downstroke. Initially, the motor 110 is rotated to cause the nut 130 to travel toward the motor 110. In this respect, rotary motion of the motor 110 is translated into reciprocating motion of the pump 100. Movement of the nut 130 also urges the plate 122 toward the motor 110, thereby retracting the diaphragm 120. Fluid such as oil in the diaphragm 120 is received by the motor seal 115.

The nut 130 also imparts a downstroke to the reciprocating arm 140, thereby increasing the size of the fluid chamber 145. As the fluid chamber 145 is increased, the pressure in the fluid chamber 145 decreases. As the pressure decreases, the pressure differential between the inside and the outside of the fluid chamber 145 increases, thereby creating a vacuum like effect inside the fluid chamber 145. The strength of the vacuum is dependent on the length of travel of the traveling valve 141. The downstroke of the reciprocating arm 140 creates a vacuum sufficient to cause the ball 141 of the traveling valve 142 to unseat so that wellbore fluids are drawn upward into the fluid chamber 145. During this time period, the standing valve 151 preferably remains closed.

After the fluid chamber 145 is filled sufficiently with wellbore fluids, the motor 110 is rotated in the opposite direction to begin the upstroke of the pump 100. The opposite rotation causes the nut 130 to reverse directions and move away from the motor 110, i.e., upstroke. This motion expands the diaphragm 120 and draws the oil away from the motor seal 115. In this respect, reciprocation of the pump 100 may be accomplished by changing the rotational direction of the motor shaft 125.

During this upstroke, the traveling valve 142 is moved closer to the standing valve 150, thereby compressing the fluid chamber 145. In turn, the pressure in the fluid chamber 145 increases, which forces the ball 151 of the standing valve 150 to unseat. Opening of the standing valve 150 allows fluids in the fluid chamber 145 to be delivered to the production tubing 20. In this manner, wellbore fluids may be delivered by positive displacement toward the surface.

In another embodiment, the reciprocating pump 700 may be driven by a hydraulic pump 715 operated by a permanent magnet motor 710. FIG. 2A shows a partial view of an exemplary hydraulically driven reciprocating pump 700. The pump 700 includes a housing 712 having one or more ports 713 for fluid communication with the wellbore 10. An expandable member 720 in the housing 712 fluidly seals off an interior portion 711 of the pump 700 from the wellbore fluids. The interior portion 711 acts as a reservoir for holding working fluid for the hydraulic pump 715. Suitable expandable members include a diaphragm and a bellow.

The expandable member 720 may be retracted or expanded using the hydraulic pump 715. An exemplary hydraulic pump suitable for use is a swash-plate hydraulic pump capable of providing high working pressure with high reliability. The hydraulic pump 715 may be driven by the permanent magnet motor 710 either directly or using a gearbox. One advantage of direct drive is reliability in long-term continuous operation. As shown, the hydraulic pump 715 and the motor 710 are immersed in the working fluid in the interior portion 711. In this respect, no motor seals are required.

The hydraulic pump 715 is connected to a piston 735 and cylinder 730 assembly adapted to reciprocate the expandable member 720. In one embodiment, the cylinder 730 includes a fluid chamber 731, 732 on each side of the piston 735. The piston 735 is extended or retracted by alternately directing the hydraulic pump output 740 into each chamber 731, 732. The piston 735 is connected to an upper portion (e.g., plate 722) of the expandable member 720 such that as the piston 735 is alternately extended and retracted, the expandable member 720 is reciprocated. Electronically operated hydraulic valves 751, 752 may be provided to control the flow of the hydraulic pump output 740 to the respective chambers 731, 732 of the cylinder 730. The electrical circuit of the valves 751, 752 may detect movement of the piston 735 and switch the valves 751, 752 in sympathy in accordance with the detected response. The piston 735 may optionally include a lower protrusion 736 to ensure the working surface on each side of the piston exerts the same force for the same injected pressure.

In operation, the motor 710 may be operated continuously in one direction to drive the hydraulic pump 715, which, in turn, may be adapted to reciprocate a reciprocating arm 140, as described with respect to FIG. 2. The hydraulic pump 715 takes in working fluid from the reservoir and outputs 740 the working fluid to the cylinder 730. In FIG. 2A, the piston 735 is in its upward stroke. As such, the lower valve 752 is energized to allow the hydraulic pump 715 to inject the working fluid into the lower chamber 732. At the same time, the upper valve 751 is de-energized to allow the working fluid in the upper chamber 731 to drain into the reservoir. In this manner, the piston 735 is urged upward to expand the expandable member 720, thereby placing the reciprocating arm 140 in an upstroke. During this upstroke, the traveling valve 142 is moved closer to the standing valve 150, thereby compressing the fluid chamber 145. In turn, the pressure in the fluid chamber 145 increases, which forces the ball 151 of the standing valve 150 to unseat. Opening of the standing valve 150 allows fluids in the fluid chamber 145 to be delivered to the production tubing 20.

When the electrical circuit detects the piston 735 is at its upper travel limit, the electrical circuit switches the valves 751, 752 in sympathy. In this respect, the lower valve 752 is de-energized to allow the lower chamber 732 to drain and the upper valve 751 is energized to allow the upper chamber 731 to fill. In this manner, the piston 735 is urged downward to retract the expandable member 720, thereby placing the reciprocating arm 140 in a downstroke. The downstroke increases the size of the fluid chamber 145, which results in a pressure decrease in the fluid chamber 145. As the pressure decreases, the pressure differential between the inside and the outside of the fluid chamber 145 increases, thereby creating a vacuum like effect inside the fluid chamber 145. The strength of the vacuum is dependent on the length of travel of the traveling valve 141. The downstroke of the reciprocating arm 140 creates a vacuum sufficient to cause the ball 141 of the traveling valve 142 to unseat so that wellbore fluids are drawn upward into the fluid chamber 145. During this time period, the standing valve 151 preferably remains closed. After the fluid chamber 145 is filled sufficiently with wellbore fluids, the lower valve 752 is energized and cycle restarts.

In another embodiment, a check valve is used 242, and the traveling valve 142 is eliminated. FIG. 3 shows a partial view of an embodiment of the pump 200 where linear movement of the plate 222 changes the volume of cavity 245. As the plate 222 is contracted, the pressure in the cavity 245 drops below the casing pressure, thereby opening the check valve 242 and allowing well fluids to flow into the cavity 245. The motor rotation is reversed when plate 222 reaches the bottom position. At this point, the check valve 242 closes. During the upstroke, the volume in the cavity 245 is decreased, thereby increasing the pressure of the fluid in the cavity 245. When the pressure in the cavity 245 exceeds the pressure in the tubing 20, the standing valve 250 opens to receive the well fluid in the cavity 245. The continued upstroke expels the fluid through the standing valve 250 into the production tubing 20. When plate 222 reaches the top of the stroke, the motor reverses rotation and the pressure in the cavity 245 begins to drop. At this point, the standing valve 250 closes and the pumping cycle repeats itself.

In another embodiment, the motor 310 may be coupled to two pumps 300, 400, as shown in FIG. 4. Each of the pumps 300, 400 is coupled to one side of the motor shaft 325 of the motor 310 using a ball screw type connection. In this embodiment, the motor is adapted to simultaneously actuate both pumps 300, 400. In operation, rotation of the motor shaft 325 causes the pumps 300, 400 to move in different phases of the pumping cycle. For example, if rotation of the motor shaft 325 places pump 300 in the upstroke, then pump 400 will be in the downstroke. Thus, pump 300 will be expelling fluid, while the pump 400 will be drawing in fluid. When the motor 310 reverses rotation, the pumps 300, 400 will react accordingly, e.g., change directions. Preferably, a bypass tubing 340 is used to deliver fluids from pump 400 to the production tubing 20.

One advantage of this two pump system is that clean fluid in the interior portions 311, 411 of the pumps 300, 400 can pass from the top pump 300 to the bottom pump 400. While movement of the plate 122 and bellows 120 increases or decreases the volume in the interior portion 311 in one pump 300, an equal change in volume is occurring in the other pump 400. Therefore, the motor seal 315 does not need to compensate for the changing volume in the interior portions 311, 411. It should also be noted that the fluid in the interior portions 311, 411 may be clean oil that is used to cool and lubricate the motor 310. The transfer of oil transferred from one pump 300 to the other pump 400 may provide additional cooling for the motor 310.

Referring back to FIG. 1, the pump 100 and the motor 110 may be installed in a wellbore 10 at a location below a subsurface safety valve 170. As shown, the pump 100 and the motor 110 are connected to a production tubing 20, which extends to the surface. A subsurface safety valve 170 is installed between the surface and the pump 100 as a safety measure in case the production tubing 20 is damaged. The safety valve 170 is adapted to accommodate a connection member that runs from the surface to the pump 100 without interfering with the integrity of the safety valve 170. In one embodiment, the connection member may be an electric cable 175 used to supply energy to operate the motor 110. The power cable 175 is connected to a high pressure penetrator that passes through the safety valve 170. An exemplary safety valve is disclosed in U.S. Patent Application Publication No. 2005/0077050, filed on Oct. 14, 2003, which application is incorporated by reference herein in its entirety. The subsurface safety valve 170 advantageously allows energy to be supplied to a motor located below the safety valve in order to remove liquids from the wellbore.

FIG. 5 shows another embodiment of a pump assembly 501 for lifting fluids to the surface. The pump assembly 501 includes an electrical submersible pump 500 operated by a rotary motor 510. Preferably, the rotary motor 510 may be rotated in opposite directions. The change in motor direction will cause the pump 500 to pump the fluid in the opposite direction, thereby reversing fluid flow in the pump 500.

The pump assembly 501 further comprises two pump chambers 511, 521 for accumulating formation fluids (also referred to as “pumped fluids.”) As shown, the pump chambers 511, 512 are stacked above one another. In another embodiment, the pump chambers may be positioned side by side. Each of the chambers 511, 521 is provided with a set of check valves 515, 516, 525, 526 for controlling the inflow and outflow of formation fluids. In this embodiment, inlet valves 515, 525 allow formation fluids to flow into their respective pump chambers 511, 521, and outlet valves 516, 526 allow the fluids accumulated in the pump chambers 511, 521 to flow out into the production tubing 20.

Each of the pump chambers 511, 521 are associated with a respective diaphragm 512, 522. The diaphragms 512, 522 control the volume available for retaining the formation fluid in each chamber 511, 521. The diaphragms 512, 522 are at least partially disposed within the chamber 511, 521 and are fluidly isolated from the formation fluids in the chamber 511, 521. Because the diaphragms 512, 522 are fluidly sealed from the formation fluid, inflation of the diaphragm 512, 522 will decrease the volume in the chamber 511, 521 available for accumulating formation fluids, while deflation of the diaphragm 512, 522 will increase the volume available for retaining formation fluids.

The diaphragms 512, 522 are inflated or deflated by an operating fluid pumped by the electrical submersible pump 500. The operating fluid may be a hydraulic fluid or other suitable incompressible fluid. In the preferred embodiment, the pump 500, diaphragms 512, 522, and the operating fluid form a closed hydraulic system. In this respect, the diaphragms 512, 522 share the same operating fluid, and a portion of the operating fluid from one diaphragm 512, 522 may be transferred to or from the other diaphragm 512, 522 depending on the direction of the pump 500. As a result, withdrawal of a portion of the operating fluid from one diaphragm 512, 522 will cause that diaphragm 512, 522 to deflate, while introduction of that portion of operating fluid to the other diaphragm 512, 522 will cause that diaphragm 512, 522 to inflate. In this respect, the two pump chambers 512, 522 operate at different phases of the pump cycle. In this manner, the two pump chambers 512, 522 may advantageously operate simultaneously to pump formations fluids to the surface.

In operation, the pump 500 is operated to pump operating fluid from the first diaphragm 512 to the second diaphragm 522, thereby deflating the first diaphragm 512 and inflating the second diaphragm 522. In turn, the volume of the first chamber 511 is increased. As the volume increases, the pressure in the first chamber 511 is reduced, thereby drawing in formation fluid through the first inlet check valve 515 to fill the first chamber 511. During filling, the first outlet check valve 516 is preferably closed or substantially closed. On the other hand, inflation of the second diaphragm 522 causes a reduction in the volume of the second chamber 522, thereby discharging the formation fluids accumulated in the second chamber 522. The formation fluids are expelled through the second outlet check valve 526, which leads to the production tubing 20. During this time, the second inlet check valve 525 is closed to prevent the formation fluids from returning into the wellbore.

After the second chamber 512 has expelled a sufficient amount of formation fluids, the second chamber 512 is ready for the filling phase, while the first chamber 511 is ready for the discharge phase. To make the transition, the motor 510 is rotated in the opposite direction to cause the pump 500 to pump the operating fluid in the opposite direction, thereby deflating the second chamber 521 and inflating the first chamber 511. In this respect, the diaphragm 512 in the first chamber 511 is expanded to force the accumulated formation fluids out of the chamber 511 and into the production tubing 20, while the diaphragm 522 in the second chamber 521 is retracted to draw formation fluids into the second chamber 521. In this respect, the pump 500 may be operated to alternately drive formation fluids to the surface. The use of a rotary motor that can rotate in at least two different directions provides an efficient manner of producing fluids to the surface.

FIG. 6 shows another embodiment of the pump assembly 601. In this embodiment, the pump assembly includes two pump chambers 611, 621 that are position side by side. A diaphragm 612, 622 is provided for each chamber 611, 621, and the diaphragms 612, 622 are adapted to operate in opposite phases of the pump cycle. The motor 510 and the pump 500 drive the working fluid between the two diaphragms 612, 622 to alternately inflate and deflate each diaphragm 612, 622.

To initiate the fill cycle in the first chamber 611, working fluid is moved from the first diaphragm 612 to the second diaphragm 622. Movement of the working fluid to the second diaphragm 622 initiates the discharge cycle in the second chamber 621. To discharge the accumulated fluid in the first chamber 611, the rotation of the motor 510 is reversed. In one embodiment, the motor rotation is reversed by reversing the phase sequence of the coils in the permanent magnet motor. The change in motor rotation results in a change in the flow of the operating fluid, now out of the second diaphragm 622 and into the first diaphragm 612. As a result, the first diaphragm 612 is expanded, there by forcing the accumulated formation fluid out of the first chamber 611, and the second diaphragm 622 is retracted, thereby by drawing in formation fluid to fill the second chamber 621.

In another embodiment, the diaphragms 612, 622 may be driven by the hydraulic pump 715 and motor 710 described with respect to FIG. 2A. For example, the lower chamber 732 and the upper chamber 731 may be placed in fluid communication with a respective diaphragm 612, 622. In this respect, as the working fluid is pumped to the lower chamber 732, diaphragm 612 will be expanded. At the same time, diaphragm 622 is allowed to drain through the upper chamber 731. After the upper valve 751 is energized, working fluid is pumped into the upper chamber 731 to fill diaphragm 622, while working fluid in diaphragm 612 is drained through the lower chamber 732.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A pump assembly, comprising: a rotary motor adapted to actuate a reciprocating pump.
 2. The pump assembly of claim 1, wherein the rotary motor is coupled to the reciprocating pump using a ball screw type connection.
 3. The pump assembly of claim 2, wherein rotation of the rotary motor causes a reciprocating action of the reciprocating pump.
 4. The pump assembly of claim 1, wherein the rotary motor comprises a permanent magnet motor.
 5. The pump assembly of claim 1, wherein rotation of the rotary motor causes a reciprocating action of the reciprocating pump.
 6. The pump assembly of claim 1, wherein the reciprocating pump comprises a positive displacement pump.
 7. The pump assembly of claim 1, wherein the pump assembly comprises an electrical submersible pump.
 8. The pump assembly of claim 1, further comprising a motor seal coupled to the reciprocating pump, the motor seal adapted for fluid expansion.
 9. The pump assembly of claim 1, wherein the reciprocating pump comprises a first valve and a second valve adapted to regulate flow into and out of a fluid chamber.
 10. The pump assembly of claim 9, wherein reciprocation in a first direction causes the first valve to open, thereby supplying fluid into the fluid chamber.
 11. The pump assembly of claim 10, wherein reciprocation in a second direction causes the second valve to open, thereby expelling fluid out of the fluid chamber.
 12. The pump assembly of claim 1, wherein the reciprocating pump comprises an expandable member adapted for reciprocating movement.
 13. The pump assembly of claim 12, wherein the expandable member comprises a diaphragm or bellow.
 14. The pump assembly of claim 1, wherein the reciprocating pump is adapted to discharge directly into a tubing.
 15. A method of lifting fluids from a wellbore, comprising: providing a pump assembly having a reciprocating pump actuated by a rotary motor; positioning the pump assembly in the wellbore; operating the rotary motor to actuate the reciprocating pump; and lifting fluids from the wellbore.
 16. The method of claim 15, wherein a drive member of the reciprocating pump is threadedly coupled to a motor shaft of the rotary motor.
 17. The method of claim 16, wherein rotation of the motor shaft causes the drive member to move along the motor shaft.
 18. The method of claim 17, wherein movement of the drive member causes a fluid chamber to expand or compress.
 19. The method of claim 15, wherein actuating the reciprocating pump comprises reciprocating the pump in a first direction and a second direction.
 20. The method of claim 19, wherein reciprocating in the first direction supplies fluid into a fluid chamber and reciprocating in a second direction expels fluid from the fluid chamber.
 21. The method of claim 15, further comprising reciprocating an expandable member.
 22. A pump assembly, comprising: a pump adapted to pump a fluid between at least two fluid cavities; and a rotary motor adapted to actuate the pump, wherein a flow of the fluid between the at least two fluid cavities is reversed by changing a rotational direction of the rotary motor.
 23. The pump assembly of claim 22, wherein each of the fluid cavities is expandable.
 24. The pump assembly of claim 22, wherein each of the fluid cavities comprise an expandable member.
 25. The pump assembly of claim 22, wherein the each of the fluid cavities is at least partially disposed in a chamber.
 26. The pump assembly of claim 25, wherein expansion or retraction of the fluid cavity controls the flow of a pumped fluid in the chamber.
 27. The pump assembly of claim 22, wherein the rotary motor comprises a permanent magnet motor.
 28. A method of lifting fluids from a wellbore, comprising: providing a pump assembly having a rotary motor and a fluid chamber; rotating the rotary motor in a first direction to introduce fluid into the fluid chamber; rotating the rotary motor in a second direction to discharge fluid from the fluid chamber; and lifting the discharge fluid from the wellbore.
 29. The method of claim 28, wherein the pump assembly comprises a second fluid chamber, wherein the second fluid chamber is discharging fluid while fluid chamber is accumulating fluid.
 30. The method of claim 28, further comprising discharging fluid from a second chamber while the fluid is being introduced into the fluid chamber.
 31. The method of claim 28, further comprising expanding an expandable member in the fluid chamber while fluid is being discharged from the fluid chamber.
 32. The method of claim 28, further comprising retracting an expandable member in the fluid chamber while fluid is being introduced into the fluid chamber. 